Automatic toll-serv ce trunking system



1930- v. s. THARP Er AL AUTOHATIC TOLL SERVICE TRUNKING' SYSTEM 5Sheets-Sheet Original Filed Oct. 19, 1927 -Ifiimr-s UTE-E 5TharpmJuhnMicks Oct. 7, 1930. v, s, THARP ET AL AUTOI'ATIC TOLL SERVICETRUNKING SYSTEI Original Filed Oct. 19, 1927 5 Sheets-Sheet 2 UiEITJ'i"E'Thar' and John Dzfinks Oct. 7, 1930. v s, THARP ET AL 1,777,420

AUTOMATIC TOLL SERVICE TRUNKING SYSTEM Original Filed Oct. 19, 1927 5Sheets-Sheet 3 UIETFI" EThar-p and J0 hn Inlicks 5 Sheets-Sheet 4 HIT V.S. THARP ET AL AUTOMATIC TOLL SERVICE TRUNKING SYSTEM Original FiledOct. 19, 1927 Oct. 7, 1930.

U1EIE-5Tharp and Jul-m [Blinks Oct. 7, 1930. v. s. THARP ET L AUTOIATICTOLL SERVICE TRUNKING SYSTEM Original Filed Oct. 19, 1927 5 Sheets-Sheet5 Inuen czrs UIEIEP SThar and Juhnfilficks Him.-

Patented Oct. 7, 1930 UNITED STATESPATENT OFFICE VICTOR S. THARP, OFELMHURST, AND JOHN WICKS, 0F OAK PARK, ILLINOIS, AS- SIGNOR TO RESERVEHOLDING COMPANY, OF KANSAS CITY, MISSOURI, A COB- ]?ORATION 'OF DELAWAREAUTOMATIC TOLL-SERVICE TRUNKING SYSTEM Application filed October 19,1927, Serial No. 227,130. Renewed April 4, 1930.

This invention relates to telephone systems in general, but is moreparticularly concerned with automatic telephone systems in which bothlocal and toll connections are established by means of automaticswitching mechanism, controlled by the calling party in a local connection and controlled by the toll operator in a toll connection. I w

The object of this invention is the provision of new and improvedswitching mechanisms for competing toll and local connections wherebythe toll operator in extending a toll connection to a local subscriberis informed whether the wanted subscriber is busy or idle, and if busy,whether in 'a local connection or in a toll connectiomand whereby, ifthe Wanted subscriber is busy ina local connection withanother'subscriber, she may cut in on the conversation and complete thetoll con nection and then release the unwanted subscriber from theconnection.

A particular feature of this invention resides in the production of anew and inn'iroved rotary connector for extending connections to privatebranch exchanges, which will select an idle one of a group of trunksextending to a wanted branch exchange providing an idle one exists, andwill select the first trunk engaged in the local connection, when allthe trunks of the group are busy either in local connections or tollconnections. The toll operator is signalled as to whether the connectionhas been extended to an idle trunk or a locally busy trunk, or whetherno connection has been extended at all by reason of all the trunks beingbusy in toll connections. If a connection has been extended to a locallybusy trunk. the operator is likewise able to cut in on the conversationand complete the toll connection and release the unwanted subscriberfrom the connection.

The various features of the invention will be described in detail in thefollowing specification with the aid of the accompanying drawingscomprising Figs. 1 to 6, which shows by means of the usual circuitdiagrams a schematic layout of a telephone system embodying theprinciples of the invention. The drawings-to be most easilyunderstoodshould be placed as follows: Fig. 2 to the rlght 0t Fig. 1,Fig. 3 underneath Fig. 2, Fig. 4 un derneath Fig. 3, and Fig. 5 to theleft of Fig. 4.

In Fig. 1, a subscribers station A is shown whose line terminates at theexchange in the individual lineswitch LS and is accessible in the banksof a group of connectors. The lineswitch LS may be of any suitable type,such as the well-known rotary type having no normal position and movingin one direction only. The lineswitch LS, together with other similarlineswitches, has access to a group of first selector switches such asthe first selector switch S.

Mechanically, the selector S is of the wellknown Strowger vertical androtary type. The circuit arrangement of the selector S is similar tothat of the selector shown and described in detail in the application ofJohn'I. Bellamy and Rudolph F. Stehlik, Ser. No. 167,908, filed Feb. 14,1927, with the modification of an additional relay, the function ofwhich is peculiar to this invention and will he described in detailsubsequently. The selector S together with other similar first selectorshas access to a number of groups of local second selectors, a separategroup being accessible in each level. A

The local second selector S indicated by a rectangle in Fig. 2, isaccessible to the group of first selectors containing selector S by wayof the trunk comprising conductors 201 to 203. Mechanically and also incircuit arrangement, the selector S may be of any suitable type such asshown and described in detail in the \Vicks Patent X0. 1,520,268. In thebanks of the second selectors, access is had to the number of groups ofindividual linc connectors (each group containing both local connectorsand combination toll and local connectors) and also to one or moregroups of local to tary connectors, a separate group being accessihle ineach level.

The local rotary connector LRC is'accessible to the group of localsecond selectors con taining selector S by way of tne trunk comprisingconductors 211 to 213. Mechanically, the local rotary connector BBC isof the wellknown Strowger vertical and rotary type, and in circuitarrangement it is similar to the rotary connector shown and described indetail in the Wicks Patent 1,644,968, granted Oct. 11, 1927, withcertain modifications which will be described in detail subsequent ly.The local rotary connector LRC together with other connectors has accessto a number of groups of trunks extending to private branch exchanges.

The trunk line comprising conductors 271 and 27 4 is one of a group ofthree trunks extending to the P. B. X. N and accessible to the connectorLR-C. This trunk line terminates at the main exchange in the lineswitch,LS which may be like the lineswitch LS switch and may have access incommon with" the line- S to first selectors.

In Fig. 3, a combination toll and local connector TLC is shown whichisaccessible to the group of local second selectors containing selectorS by way of the trunk comprising conductors 301 to 303, and isaccessible to a group of toll second selectors (to be mentionedsubsequently) by way of the trunk comprising conductors 304 to 307.Mechanically, the toll and local connector TLC is of the well-knownStrowger vertical and rotary type. The circuitarr'angement of theconnector TLC forms a particular part of this invention and will bedescribed in detail sub-' sequently. The connector TLC, together withother connectors, has access to individual subscribers lines, such asthe line comprising conductors 101 and 103 extending to substation A,and the line comprising conductors 61 and 63 extending to substation A.T he line of substation A also terminates ina lineswitch (not shown)which may be similar to the lineswitch LS and may have access to firstselectors in common therewith.

In Fig. 5, the calling end of the toll operators cord circuit 0,terminating in the plug P and equipped with a listening key K and adialling and ringing key K, is shown. The dial D may be associated'withcord circuit 0 by operating the key K to the right. The cord circuit 0may be of any suitable type and is therefore not shown in full; onlythose elements which concern the invention are shown.

The toll operator has access to a group of toll transmission selectorsby way of trunk lines accessible at jacks at her position. The tolltransmission selector TTS is accessible at the toll operatorsswitchboard at jack J via the trunk line comprising conductors 3 and 4.Mechanically, the toll transmission selector TTS is of the well-knownvertical and rotary type, and has access in its bank to a number ofgroups of toll second selectors, a separate group being accessible ineach level. The circuit arrangement of the toll transmission selectorTTS forms a particular-part of this invention and will be described inde tail subsequently. a

The toll second selector TS, indicated in in that level.

Fig. 5 by a dotted rectangle, is accessible to the toll transmissionselectors by way of the trunk comprising conductors 505 to 508.Mechanically, and also in circuit arrangement, the selector TS may be ofthe wellknown vertical and rotary type similar to the local secondselector S, except that the ring- TLC shown in Fig. 3 is accessible tothe.

oup of toll second selectors containing seector TS by way of trunkconductors 304 to 307. v

The toll rotar connector TRC is accessible tothe group of toll secondselectors containing selector TS by way of trunk conductors 405 to 408.Mechanically, the toll rotary connector TRC is of the well-knownvertical and rotary type. The circuit arrangement of the connector TRCforms a particular part of this invention and will be described indetail presently. The banks of the toll rotary connectors are multiplyconnected with the banks of the corresponding local rotary connectors.Thus the toll rotary connectors have access in common with the localrotary connectors to the groups of trunk lines extending to the privatebranch exchanges.

Fig. 6 comprises five diagrams 6 to (S which show the various testpotentials existing on the test contacts of the trunks to a privatebranch exchange under different cir-' cumstances. I

IrVith this general descri tion of the objects of the invention and t eapparatus involved in mind, a detailed description of the y operationwill now be given. ,For this purpose, it will first be assumed that thesubscriber at substation A desires connection with the subscriber atsubstation A. To complete this connection, the subscriber at substationA removes his receiver and dials the directory number of the subscriberat substation A. Responsive to the removal of the receiver at substationA, lineswitch LS erates in the usual manner and extends the connectionto an idle first select-or which will be assumed to be selector S.Responsive to the dialling of the first digit of the called number,selector S operates to raise its wipers opposite the level of bankcontacts corresponding to the digit dialled, and then automaticallyselects an idle trunk accessible (A detailed description of the verticaland rotary operation of a selector similar to selector S is given in theapplication of John I. Bellamy and Rudolph F. Stehlik, Ser. No. 167,908,referred to above.) The windings of relay 21 of selector S are includedin the talking circuit, but are wound differentially so that relay 21 isnot operated when current flows through both its windings in series withthe line relay oi the succeeding switch.

Responsive to the second digit dialled by the calling subscriber, secondselector S opcrates in the regular manner'andextends the connection tothe first idle connector of the group accessible in the level of bankcontacts corresponding to the digit dialled.

It is assumed that the connector selected is the toll and localconnector TLC shown in Fig. 3, accessible by way of trunk conductors 301to 303. When the connection is extended to the connector TLC, line relay311 operates and prepares the connector for oporation. Responsive to thedialling the third digit, vertical magnet 321 operatoand raises theswitch wipers opposite the corresponding level of the bank contactsunder the control of line relay 311, series relay 319 operating inseries with magnet 321. At the end of the vertical movement, relay 319deenergizes and by closing contacts 389, closes the circuit for thecombination changeover and meter control relay 314, the circuitincluding vertical oft normal springs closed upon the first step of theswitch wipers. Relay 314, inoperating, places rotary magnet 322 in theimpulsing circuit instead of vertical magnet 321 by closing contacts.345 and separating contacts 346, andloy separating contacts 34.2 andclosing contacts 343 prepares the circuit over which the boosterbattery, BB will later be applied to the release conductor 302.

Responsive to the dialling of the last digit by the calling subscriber,rotary magnet 322 operates and rotates the switch wipers into engagementwith the set of contacts terminating the line to substation A. If theline is busy, busy rela 318 operates in the usual manner (over its lowerwinding-its upper winding has no utility in this type of call) and givesthe calling subscriber the busy signal. It the line is idle, switchingrelay 320 operates when relay 319 falls back and performs its usualcircuit changes. including the closing of the signalling circuit atcontacts 391 and 398, and the connection of ground potential to theprivate contact 612', in this case. through contacts 336 of relay 312thereby shunting resistance R. I

When the subscriber at substation A answers, ring cutoff 221 operatesand trips the ring and completes the talking circuit, after whichback-bridge relay .310 is energized in series with the windings ofdifferential relay 313. Relay 313, being differentially wound, does notoperate at this time. Backbridge relay 310, however, operates and opensthe holding circuit for relay 314 by separating contacts 331, and byclosing contacts 324,

releases, after which direct ground potential is connected again torelease conductor 302, viacontacts 335, 342 and 324. In this type ofconnection, relays 315 :1nd 316 are not operated, and the operations ofthe connect 1' TLC are similar to the general connector operationswell-known in the; art, with the exception of the operations concerningrelay 314 which have been described in detail. The release of theconnection at the termination of the conversation takes place in theusual manner responsive to the replacement of the receivers of the two,subscribers.

From the foregoing description, it should he noted that when onesubscriber completes call to another subscriber the rivate normalcontacts of both the calling inc and the called line are groundeddirectly and according to this invention are thus marked local- 1y busy;that talking current is furnished to the calling subscriber through thewindings of the line relay of the connector used in the connection inseries with the windings of a differential relay in the first selector,the latter relay by reason of its differential characteristic not beingoperated; and that talking current is furnished to the called subscriberthrough the windings of the back bridge relay in the connector in serieswith the windings of a differential relay in the connector, the latterof which likewise by reason of its differential characteristic is notoperated.

To further describe the invention, it will now be assumed that the tolloperator has received a-toll call from a distant point for thesubscriber at substation A. To com lete the call, the toll operatorinserts the ca ling plug of a cord, plug P of the cord 0 for example,into the jack of an idle trunk such as jack J. Inserting plug P intojack J places a bridge across trunk conductors 3 and 4, thereby closinga circuit for the upper winding of line relay 24 which extends fromground at contacts 33 and includes trunk conductors 3 and 4 and contacts36, 35, 69 and 98 in series. Line relay 24 operates and closes a pointin the talking circuit at contat-ts 83 and closes the circuit of releaserelay 25 at contacts 89. Relay 25 operates and grounds the releaseconductor 99 at contacts 91, prepares the impulsing circuit at contacts92, and closes a circuit for the lower winding of switch-over-controlrelay 13 at contacts 94, this latter circuit also including contacts 78,49, 84 and 40. Relay 13 operates and .opens a point in the circuit ofswitch-over relay 12 by separating contacts 43 and prepares a circuitfor relay 14 at contacts 42.

After inserting plug P into jack J, the toll operator throws key K tothe dialling position and then dialsthe directory number of prisingconductors 304 tof307, terminating the subscriber at substation A, afterwhich in the toll and local connector TLC. When she again restores key Kto normal. this trunk line is seized, the line relay of the Responsiveto the first digit dialled, vertitoll second selector TS is disconnectedfrom cal ma net 29 of the toll transmission selecthe talkin conductors(by the" operation of tor T S operates and raises the switch theswitching relay of the selector TS) and a wipers opposite thecorresponding level of new circuit'is established for the upper windbankcontacts, after which rotary magnet 30'ing of the relay 13 through thewindings operates under the control of stepping-relay of the line relay311 ofwonnector TLC.

27 and rotates the wipers into engagement Thus relay 13in the tolltransmission selecwith the set of bank contacts'terminating an tor TTSis now maintained energized over idle trunk. After the trunk selecting'operits upper winding inseries with the line reation, switching relay23 operates and perlay 311 of connector TLC. Line relay 311 forms itsusual circuit changes including the also operates over this circuit andrepares closing of points in the talking circuit at conconnector TLC foroperation as escribed tacts 80 and 87, the connecting of thegroundpreviously.

ed release conductor 79 to test wiper 502 at Line relay 24 of the tolltransmission seleccontacts 82, and in addition, grounds the tor TTSagain operates responsive to the prepares another circuit for the lowerwindring-control 100.by closing contact 83, opens dialling of the thirddigit, opening the cirthe initial holding circuit for the lower windcuitof line relay 311 of connector TLC a coring of relay 13 by separatingcontacts 84 and responding number of times, causing the operation ofVertical magnet 321 to step the ing of relay 13 by closing contacts 85.The wipers of the switch opposite the correspondoperation of the tolltransmission selector ing level of bank contacts. Series relay 319 TTSin regard to its vertical and rotary again operates in series withvertical magmovement is similar to the regular selector net 311, and atthe end of the vertical moveoperation well-known in the art. A detailedment deenergizes, again closing the circuit of description is thereforedeemed unnecessary. relay 314 at contacts 389. Relay 314 oper- It isassumed that the trunk selected'is the ates, closing a locking circuit'for itself at one comprising conductors 505 to 508, termicontact 344and disconnecting the vertical nating in the toll second selector TS.When magnet from the impulsing circuit by sepathis trunk line is seized,a circuit for the line rating contacts 346 and connecting the rorelay(not shown) of the toll second selector tary magnet thereto by closingcontacts 345, TS is closed, which includes the upper windand in additionthereto, closes a circuit for ing of relay 13, contacts 38, the tworight hand the reverting control relay 316 by closing conwindings of therepeating coil RC,c0ntacts 46 tacts 341, ground being present on thering and 44,conductors 8 and 6, and conductors 505 control conductor 306(connected via conand 508 in series. Relay 13 is now held open ductor507 to conductor 100) Relay 316 ated over this circuit, the initialcircuit for its operates and opens its initial energizingcirlowerwindingha-vingbeen opened at contacts cuit by separatingcontacts 367 and closes 84. Relay 13 is made slow-acting to prevent alocking circuit for itself to the grounded its dropping back during theshort interval toll release conductor 305 by closing contacts after thecircuit of its lower windingis opened 366, prepares a circuit forenergizing the and before the circuit including its upper two-stepconverting relay 315 to its first winding and the line relay of the tollsecond step by closing contacts 369, closes a circuit selector TS isestablished. for the upper winding of ring cut-ofi' relay Line relay 24again operates responsive to 317 at contacts 368, and prepares theholding the dialling of the next digit, and at each decircuit for thering cut-off relay 13 by closenergization opens the circuit of the linereing contacts 364. Ring cut-off relay 317 lay of the toll secondselector TS at contacts energizes and closes its holding circuit to 88.The toll second selector TS operates in the ring control conductor 306at contacts the usual manner and raises its Wipers OppO- 371, openspoints in the ringing circuit by site the level of bank contactscorresponding separating contacts 370 and 377, and perto the digitdialled and .then'selects an idle forms other circuit changes which willbe detrunk in that level. A circuit is also closed scribed presently.for the lower winding of relay 13 each time Responsive to the last digitdialled by the line relay 24 deenergizes, this latter circuit tolloperator, rotary magnet 322 operates and including contacts 90, 92, and85. Thus rerotates switch wipers into engagement with lay 13 ismaintained energized over its lower the bank contacts terminating theline to subwinding during the intervals when the cirstation A. Duringthe rotary motion, recuit of its upper winding is opened to operate lay319 operates in series with rotary magthe toll second selector TS sothat relay 24 is net 322 and connects the test relay 318 to themaintained energized continuously. test wiper 602 at contacts 385 andcloses the It is assumed that the trunk selected by energizing circuitof the lower winding of the toll second selector TS is t e one comthetwo-step converting rel y 317 at contacts 388, the latter circuit alsoincluding contacts 339, 356, and 369. Relay 315 operates to its firststep to close contacts 355, thereby preparing the circuit over which itenergizes to its second step when-contacts 388 are again opened.

The called line may be busy in a toll or local connection. in which casetest relay 318 cuergizes, but it will first be assumed that the calledline is idle at this time. At the end of the rotary movement, relay 319falls back and by separating contacts 388 causes relay 315 to operate toits second step to perform the following changes: By the separation ofcontacts 347 and 360, back-bridge relay 310 and differential relay 313,whose windings are connected in series with the windings of theback-bridge relay 310, are disconnected from the talking conductors. Bythe separation of contacts 349 and 361, line relay 312 is disconnectedfrom the talking conductors. By the closure of cont-acts 348 and 359,points in the talking circuit are closed. A point in the circuitofrelease magnet 323 is opened by the separation of contacts 350. Releaseconductor 302 extendingto'the banks of the local selectors is groundedat contacts 351. A circuit is closed including the two windings of testrelay 318 in series at contacts 352, but relay 318, being differentiallywound, is not operated. A circuit over which the operation of the tolltone relay 18 in the toll transmission selector TTS is controlled isprepared at contacts 355 ;'and

a circuit for the lower Winding of switching relay 320 is closed torelease conductor 305 at contacts 354. Switching relay 320 operates andperforms its usual circuit changes including the closure of points inthe talking circuit at contacts 391 and 398 and the plac ing of groundpotential on the private normal contact 612 of the called subscribersline by the closure of contacts 392. In this case, however, ground isconnected to the private test contact of the called line throughresistance R rather than being connected directly, since line relay 311and then release relay 312 restore after relay 311 is disconnected fromthe talking conductors, as a result of which contacts 336 are opened. Inthis manner the line at substation A is marked toll busy asdistinguished from being marked locally busy when direct ground isconnected to the private normal contact, the purpose of which will bedescribed sub-- sequently.

\Vhen line relay 311 is disconnected from the talking conductors, thecircuit over which the upper winding of relay 13 in the tolltransmission selector TTS is held energized is interrupted. This relaythereupon deenergizes and completes the circuit for the switchover relay12 by closing contacts 43, oif-norinal springs 10 having closed upon thefirst vertical step of the switch wipers. Relay 12 energizes and byseparating-contacts 33 and 35 and closing contacts 34 and 36 reversesthe direction of current flow over trunk conductors 3 and 4, the upperand lower windings of the line relav 24 now being connected to trunkconductors 3 and 4, respectively. At contacts 40 a point in the circuitof the lower winding of relay 13 is opened. By the sep aration ofcontacts 38, another point in the circuit of the upper winding of relay13 is opened and by the closure of contacts 39, battery feed relay 20 isconnected to trunk conductor 8 via the upper right hand winding ofrepeating coil RC. By the closure of contacts 41, ground feed relay 21is connected to trunk conductor 6 via the lower right hand winding ofrepeating coil RC. By the separation of contacts 37, the short circuitaround the upper left hand winding of re peating coil RC is removed, andby the closure of contact 37 the upper and lower left. hand windings ofthe repeating coil RC are connected via the condenser. Due to thereversal of current flow over the trunk conductors 3 and 4, polarizedrelay 2 in the operators cord circuit 0 energizes andcauses the lightingof the lamp L.

The lighting of the lamp L at this time indicates to the toll operatorthat an idle line has been connected with and that she may signal thecalled subscriber as soon as she is ready. To signal the calledsubscriber, the toll operator throws the key K to the leftvto applyringing current to the trunk conduc tors. Ringing relay 11, which isbridged across the trunk conductors 3 and 4, responds to ringing currentand closes the circuit of relay 22 at contacts 32. Relay 22 operates andby separating contact 78, disconnects ground from the ring controlconductor 100 connected via conductor 507 to the ring control conductor306 to which ring cut-01f relay 317 in the toll and local connector TLCi is locked. As a result, ring cut-01f relay 317 deenergizes and bypermitting contacts 370 and 377 to close, starts the regular automaticinterrupted ringing to signal the called subscriber. Belay 22 inoperating also closes a local holding circuit for line relay 24 byclosing contacts 76 to maintain relay 24 energized while ringing currentis applied to trunk conductors 3 and 4.

\Vhenthe called subscriber answers, ring cut-off relay 317 operates,being energized over its lower winding over the called line loop in theusual manner, and again closes its locking circuit to conductor 306 atcontacts 371, and closes pointsin the talking circuit at contacts 371and 376. After the ring cutoff relay 317 is operated, both relays 20 and-21 of the toll transmission selector TTS enertors 3 and 4 by separatingcontacts 67 and 69,

' guishes the lamp L. The extinguishment of lamp L notifies the tolloperator that the called subscriber has answered. After receiving thissignal, the toll operator takes necessary steps to complete the talkingconnection between the calling and the called subscriber, after whichthe two may hold conversation.

When the subscriber at substation A replaces his receiver at thetermination of the conversation, the circuit of relays 20 and 21 isinterrupted. Relay 20, in deenergizing, reconnects the windings of linerelay 24 to trunk conductors 3 and 4, thus again establishing thecircuit of polarized relay 2 in the operators cord circuit. 0. Relay 2in energizing lights lamp L. The lighting of the lamp L at this timeindicates to the tool operator that the called subscriber has replacedhis receiver whereupon she will remove plug P from jack J, to releasethe switches used in the connection.

Removing plug P from jack J opens the circuit of line relay 24, whichthereupon deenergizes and opens the circuit of release relay 25. Relay25 deenergizes and disconnects ground from release conductor 99 byseparating contacts 91, thereby opening the circuit of switching relay23, the switching relay of selector TS, and the holding circuits ofrelays 315, 316, and 320 of the connector TLC, whereupon these relaysdeenergize and restore to normal. Switching relay 23, in deenergizing,disconnects ground from ring control conductor 100 by separatingcontacts 83. The removal of ground from ring control conductor 100 opensthe holding circuit of ring cut-off relay 317 of the connector TLC.Relays 315 and 320, in restoring, close a circuit for release magnet 323by closing contacts 350 and contacts 397, re-

spectively. Release magnet 323 thereupon operates and restores theswitch wipers to 0 normal. The release of the switching relay of theselector TS also initiates the release of the wipers of'the selector TS.The closure of contacts 90 by the release of line relay 24 also closesthe circuit of release magnet 31, vertical off-normal springs 9 havingclosed upon the first vertical step of the switch wipers. Magnet 31operates and restores the switch wipers to normal. All the switches usedin the above-described connection are now in their normal condition andare ready to be used in the establishment of other connections.

In accordance with one of the principles of the invention, the operatorin attempting to establish a toll connection is able to complete tiontothe connector TLC via the cord cir-- cuit O, toll transmissionselector TTS, and toll second selector TS, and that the wanted line tosubstation A is busy at this time. As soon as the wipers of theconnector TLC are rotated into engagement with the contacts terminatingin the line to substation A, test relay 318 is energized over its lowerwinding from ground potential either direct, or through a resistance asR depending upon whether the line is locally busy or toll busy) on thetest contact 612'. Relay 318 operates and prepares a locking circuit foritself at contacts 379, opens a point in the circuit over whichswitching relay 320 will later be energized by separating contacts 381,connects conductor 308 connected to interrupter I '(Fig. 4) to the trunkconductor 307 at contacts 383, and prepares the circuit over which theoperation of the tone control relay 18 in the toll transmission selectorTTS is controlled at contacts 378. I

Shortly after the termination of the rotary motion, relay 319deenergizes and permits converting relay 315 to operate to its secondstep and perform the circuit changes, as previously described, closesthe locking circuit for the lower winding of relay 318 to the ringcontrol conductor 306 by permitting contacts 386 to close, and furtherprepares the circuit over which the operation of tone control relay 18is controlledby permitting contacts 384 to close, that is, connects testwiper 602, via contacts 378 and 355, to trunk conductor 304. Both relays317 and 318 are now locked to the ring control conductor 306. It shouldbe noted'that no current flows in the upper winding of relay 13 at thistime, since ground is connected to both terminals thereof. U

The disconnection of line relay 311 from the trunk conductors againcauses the deenergization of relay 13 in the toll transmission selectorTTS and as previously described causes the current flow over the trunkconductors 3 and 4 to be reversed, and causes relays 20 and 21 to beconnected to conductors 8 and 6 respectively, the former operation re-20 in the toll transmission selector TTS. Re-

lay 20 therefore operates accordingly, disconnecting the windings ofline relay 2.4 from the trunk conductors 3 and 4 by separating contacts67 and 69 each time it energizes, thus intermittently opening andclosing the cir-' cult of the polarized relay 2 in the operatorscordcircuit 0. This causes the lamp L to flash, which signal indicatesto the toll operator that a busy condition has been encountered.

for relay 19 at contacts 69 "via the normally closed contacts 72 ofrelay 2'1. Relay 19, in operating, closes a locking circuit for itselfat contacts 64 fronrground at the vertical offnormal springs 10 viacontacts 59, and closesthe closure of contacts 63, relay 15 instead of.

relay 22 is placed under the control of ringing relay 11. At contacts65, relay 18 is connected via contacts 57 and 48 to the lower trunkconductor 6.

If now the called line is busy in a local connection, directground-potential is present on the test contact 612 engaged by testwiper 602, which is now connected via contact 384 and 378 to trunkconductor 304 connected to trunk conductor 6. Thus relay 18 is shortcircuited and remains unoperated. But if the" line to substation A isbusy in a toll connection, ground potential is connected to the testcontact 612 through a resistance such as resistance R in the connectorused in the other toll connection. In such case, sufiicient current iscaused to flow through relay 18 from battery via resistance R connectedto trunk conductor 304 via contacts 363 to cause it to operate. Relay18, in operating, connects conductor 9, to which a characteristic tonecurrent is applied, to the trunk conductor 6. This tone current, passingthrough the lower right hand winding of repeating coil RC and throughthe winding of relay 20, is induced in the left hand windings of repeating coil RC.

The toll operator upon perceiving. the flashing of the lamp L, operatesher listening key K1, providing it is not not already operated, toconnect her headset across the trunk conductors for the purpose ofdetermining whether the wanted line is busy in a toll connection or in alocal connection. If she hears the special tone, she understands thatthe wanted line is busy in a toll connection whereupon she will removethe plug P from the jack J to release the connection she has set up,with. the intention of attempting to establish a connection at somelater time.

If, however, the toll operator bears no tone, it indicates to her thatthe wanted line is busy in the local connection. The toll operatorthereupon momentarily operates the key K to the left, thereby applyingringing current to the trunk conductors 3 and 4 and causing theoperation of the ringing relay 11 in the Relay 20, in operating, alsocloses a circuit,

toll transn'iission selector TTS. Relayll, in

operating, closes the circuit of relay 15. Rei second step as soon asconta .tS 47 are again separated. Relay 1.5 also esta lishes a localholding circuitfor line relay 24 at contacts 51 while ringing current isbeing applied to the trunk conductors 3 and and opens the ductor 100.This removes the short circuit from the upper winding of busy relay31.8. The Values of resistance R5, and the resistance of the upperwinding of ringcut-oll' relay 317 and each of the windings of test relay318 are approximately equal, by reason of which a balanced Wheatstonebridge is now formed with equal values of the current flowing in boththe upper and lower windings of test relay 318. Since the windings ofrelay 318 are differentially wound, relay 318 now deenergizes. Indeenergizing, relay 318 opens the circuit of its lower winding byseparating contacts 380, disconnects conductor 308, connected to theground interrupter I, from the talking conductor 307 by separatingcontacts 383, disconnects wiper 602 and also battery through resistanceR from talking conductor 307 by separating contacts 378, and by closingcontacts 381 closes a circuit via contacts 354 for switching relay 320.Relay 320 now operates and performs the circuit changes previouslydescribed, including the closure of the talking circuit by closingcontacts 391 and 398.

After key K is restored, relay 11 and, a moment later relay 15, restore.Two-step relay 16 operates to itssecond step and closes a lockingcircuit for itself at contacts 53 via contacts 59 and verticaloff-normal springs 10, prepares an energizing circuit for two-step relay17 at contacts 54, grounds ring control conductor 100 at contacts 58,opens a point in the circuit of tone control relay 18 at contacts 57,and prepares the bridge by which ground will later be connected to thetwo trunk conductors at contacts 52 and 56.

The operator is now able to converse with the wanted subscriber and willinform him that there is an awaiting toll call for him, and will alsoinform the unwanted subscriber that he will be disconnected from theconnection. The operator thenoperates the key K momentarily to theringing position a second time. Ringing relay 11 again responds, andinturn, causes the operation of relay 15. By the closure of contacts 46and 44 ground potential is now applied to both conductors 8 and 6. Bythe closure of contacts 47, an energizing circuit for the lower windingof short circuit around resistance R5 by separatin g contacts 49,thereby removingthe direct ground potential from the ring control con-'two-step relay 17 is closed, causing this relay to operate to its firststep and prepare an energizing circuit at contacts 59 over which it willoperate to its second step as soon as con tacts 17 are again separated.

busy in a local connection in which he is the called party, theplacement of ground 'potcn tial on both conductors 8 and 6 shortcircuits a winding of the back-bridge relay and a winding of thedifi'erential relay in the connector used in the local connectioncorresponding to the lower winding of relay 310 and the lower winding ofdifferential relay 313 of connector TLC. The interruption of current inone winding of the differential relay in the connector used in the localconnection causes that relay to operate and close at contacts whichcorrespond to contacts 340 the circuit for the release magnet of thatconnector. The release magnet operates and restores the wipers of theconnector to normal. Thus the unwanted subscriber isdisconnected from hesubscriber who is wanted in the toll connection. I

Finding himself disconnected, the unwanted subscriber will then replacethe receiver, if he did not when informed of the incoming tollconnection for the other subscriber, thus causing the release of theother switches used in the local connection. Had the unwanted subscriberreplaced his receiver as seen as the toll operator informed the twoparties of the awaiting toll call, all but the connector used I in thelocal connection would have been released at that time. In either case,however, the connector used in the local connection is released as abovedescribed.

When relay 15 falls back at the end of the second momentary operation ofkey K to the ringing position, two-step relay 17 operates to its secondstep, and by separating contacts 59, opens the holding circuit fortwo-step 16 and relay .19. Relay 19, in deenergizing, opens the circuitof relay 14 at contacts 66, opens another point in the circuit of tonecontrol relay 18 at contacts 65, opens another pointin its own lockingcircuit at contacts 64, and replaces relay 22 under the control ofringing relay 11. Relay 14, in deenergizing, again connects relay 21totrunk conductor 6 by closing contacts 15.

If the Wanted subscriber has maintained his receiver to his ear, as heis expected to do, relays 20 and 21 will now energize, with the resultas previously described, lamp L remaining extinguished. If, however, thewanted subscriber has also replaced his receiver, relays 20 and 21 willnot be energized and the lamp L=will light. The toll operator mayresignal the wanted subscriber by operating key K to the right a thirdtime and thus cause relay 22 to operate and remove ground from ringcontrol conductor 100. This starts the regular automatic ringing bycausing the deenergization of the ring cut-off relay 317 in the toll andlocal connector TLC, which relay ,a-gain operates upon the removal ofthe receiver at the called station, whereupon the talking connection iscompleted. Assuming that the wanted subscriber is In the above case itwas assumed that a combination toll and local connector was used in thelocal connection. It is understood of course, that each group ofindividual line connectors comprises both local connectors andcombination toll and local connectors, the local connectors beingsimilar to the connector TLC, with relays 315 and 316 omitted. A localbusy connector is released by the toll operator in the same manner as isa combination toll-and local connector when used in a local connection.

In the above case it was assumed that the wanted subscriber was engagedin a local connection which he initiated. If the wanted subscriber isbusy in a local connection in which he is the calling party, the tolloperator may likewise intrude and release the unwanted subscriber fromthe connection. In such a case, the application of direct groundpotential to the two trunk conductors, resulting from the operatorsactuating her ringing and dialing key to the ringing positionmomentarily the second time to release the unwanted subscriber from theconnection, operates on the first selector used in the local connectionrather than on the connector.

To describe the manner in which a first selector in such a connection isoperated upon,

let us assume that the toll operator has ex- 1 which he initiated viathe selector S. As will be recalled from the local connection previouslydescribed, the differential relay 121 remained deenergized. Theapplication of direct ground potential to the two toll talkingconductors responsive to the second' momen tary operation of theringingand dialing key to the ringing position in the present caseshort-circuits the winding of differential relay 121 which is connectedin series with the grounded winding of the line relay of the connectorused in the local connection, whereupon relay 121 operates and closesthe circuit of release magnet 122 at contacts 123. Release magnet 122operates and opens points in the talking circuit of the local connectionby separating contacts 124 and 125, thereby causing the release of thesucceeding second selector switch, and also restores the wipers ofselector S to normal. Switching relay 120 of selector I S is maintainedoperated over the circuit extending frrom the release conductor 112connected to release conductor 102 to which ground potential is nowapplied in the toll and local connector used in the toll connectionthrough a resistance such as resistance R, through the winding ofswitching relay 120,

contacts 131, 132, through the winding of stepping relay 119 to battery.The connector used in the local connection is released when the calledsubscriber, finding himself disconnected, replaces his receiver.

As described in the introduction of the specification, a particularfeature of this invention is the production of the toll rotary connectorTRC, Fig. 4, which, when used by the toll operator to extend a tollconnection to a private branch exchange, selects an idle trunk line ofthe group extending thereto, providing an idle one exists, or selects alocally busy line, providing all the trunks are locally busy or tollbusy, after which the toll operator is able to force the release of theexisting connection over the selected locally busy trunk line. In orderto accomplish the latter operation, local rotary connectors such as thelocal rotary connector LRC shown in Fig. 2 are required. The manner inwhich these operations are accomplished will now be described, and forthis purpose, it will be assumed that the toll operator wishes to extenda connection to the private branch exchange N, and has set up aconnection via-the cord circuit 0, the toll transmission selector TTS,and the toll selector TS, to the'toll rotary connector TRC.

When the connection is extended to connector TRO, line relay 411operates and grounds conductor 406 at contacts 432, and closes a circuitfor the lower winding of ring cut-01f 412 at contacts 433. Relay 412energizes and at contacts 437 closes a locking circuit for itself to thering control conductor 407, to which ground is applied in the tolltransmission selector TTS, closes points in the talking circuit atcontacts 436 and 440, and prepares the impulsing circuit at .contacts438.

Responsive to the operators dialing the next digit, vertical magnet 421operates under the control of line relay 411 and raises the switchwipers 481 to 484 opposite the level of bank contacts in which thetrunks to the P. B. X. N are-accessible. The relay 413 operates inseries with magnet 421, maintaining the vertical magnet circuit closedat contacts 442, vertical off-normal springs 472 opening and springs 472closing on the first Vertical step of the switchwipers. At the end ofthe vertical movement relay 413 falls back and prepares the circuit ofthe rotary magnet 442 by closing contacts 443.

Responsive to the dialing of the next digit by the toll operator, rotarymagnet 422 opcrates and rotates the switch wipers into engagement withthe set of contacts terminating the first trunk in the-group of trunklines extending to the P. B. X. N.' Relay 415 energizes in series withmagnet 422, and closes a circuit for relay 417 at contacts 449, closes acircuit for relay 416 at contacts 450, and opens a point in the circuitof the lower wind ing of relay 418 at contacts 451.- Relay 416 4 circuitof the lower winding of relay 418 at contacts 456. Relay 417 energizesand closes a point in the circuit of stepping relay 420 at contacts 457,prepares the circuit for the energizing windlng of diflerential busyrelay 414 at contacts 459, and at contacts 416 closes the initialenergizing circuit of twostep relay 410, causing this relay to operateto its first step and prepare an energizing circuit at contacts 426 overwhich it will operate to its second step as soon as contacts 460 areagain opened. a

In the system shown in the drawings, it has been assumed that threetrunks comprise the group extending to the P. B. X. N the last of whichcomprises conductors 271 to 274 accessible at bank contacts 488, 489,489, an 490, and terminating at the P. B. X. N in the jack J. The twotest contacts for each trunk are connected together by resistances,contacts 489 and 489' being connected by resistance R93. Each of theupper test contacts, such as contacts 486, 487, and 489, are connectedto a chain relay which is operated when the trunk is busy. When all ofthe chain relays of one group of trunks are operated, a chain circuit isclosed to connect battery through a resistance to the upper test contactof the first trunk of the group. No trunk is connected to the set ofcontacts immediately following the set terminating the last trunk of thegroup, but is equipped as follows: Contact 491 is connected to theground interrupter I, contact 492 is connected to ground throughresistance RA94, and bank contact 493 is connected to battery throughresistance R96.

Fig. 6 shows the various test potentials which exist on the testcontacts of the trunks under difierent conditions. Resistances a and 12represent the switching relay of the lineswitch terminating the trunkand the chain relay of the trunk, respectively. When a trunk is idle,both test contacts are free from ground potential as shown at 6 Fig. 6.When a trunk line is busy in a local connection, direct ground potentialis connected to the upper test contact as shown at 6 Fig. 6. When atrunk line is busy in a toll connection, direct ground potential isconnected to the upper test contact and ground through a low resistanceis also connected to the lower test contact as shown at 6, Fig. 6.

To continue with the description of the operation of the connector TRC,it will be assumed first, that one of the lines of the group, namely,the line comprising conductors 271 to 274, is idle at this time, theother two trunk lines being busy either in a toll connection or in alocal connection. Since this trunk line is idle, chain relay 496 is in adeenergized'position, and battery through to resistance R95 is notconnected to contact 486'. Shortly after the-termination of the rotarymotion, relay 415 falls back and opens the circuit of relay 416 atcontacts 450, opens the initial circuit of relay 417 at contacts 449,closes a holding circuit for relay 417 at contacts 448, and closes aoint in the circuit of the lower winding of re ay 418 at contacts 451.In the case assumed, relay 418 is not sufliciently energized to causeits operation, and it therefore remains deactuated. Shortly after thecircuit of relay 416 is opened, this relay deenergizes and a circuit isclosed at contacts 453 for stepping relay 420 which extends from groundon test contact 486, wiper 482, contacts 461, 457, 453, 471, through thewinding of stepping relay 420 to the battery. Relay 420 energizes andcloses a holding circuit for itself to the release conductor 406 atcontacts 469, andcloses a circuit for rotary magnet 422 at contacts 470,at the same time closing a holding circuit for relay 417 which includescontacts 454 and 448. Magnet 422 operates and rotates the switch wipersinto engagement with the bank contacts terminating the second trunk.Magnet 422, in operating, also opens the holding circuit of relay 420 atcontacts 471. Relay 420 thereupon deenergizes and opens the circuitofrelay 417 and magnet 422 at contacts 470. Since it is assumed thatthis trunk line is also busy, ground potential is also present oncontact 487, and stepping relay 420 again energizes, again causing theoperation of magnet 422 as previously described, the switch wi ers beingrotated into engagement with the ank contacts 488, 489, 489, and 490.Since no ground potential is present on bank contact 489, this trunkbeing idle, stepping relay 420 is not operated, and the switch Wipersare arrested in this osition.

A er an interval, relay 417 falls back, opens a point in the circuit ofrelay 420 by separating contacts 457, and by separating contacts 460,permits two-step relay to operate to its second step. By the separationof contacts 424 and 431, line relay 411 is disconnected from the trunkconductors. By the closure of contacts 425 and 430, points in a talkincircuitare closed. At contacts 429 groun through resistance R isconnected via wiper 483 to test contact 489 (and the contacts multiplyconnected therewith). By the closure of contacts 427, a circuit isestablished for the two windings of test relay 414 and for switchingrelay 419; Relay 414 is differentially wound, and therefore is not0perated. Switching relay 419 operates and connects direct ground totest contact 489 at contacts 466 via Wiper 482, and closes points in thetalking circuit at contacts 465 and 468. The disconnection of line relay411 from the trunk conductors again initiates the signalled by thelighting of the lamp L, which indicates that connection has beenestablished with an idle trunk. To intitiate the signaling of theattendant at the privatebranch exchange, the toll operator operates keyK to the ringing position, which causes the ring cut-off relay 412 inthe connector TRC to unlock by removing ground potential from the ringcontrol conductor 100. Relay 412, in releasing, closes the signallingcircuit at contacts 441 and 435, causin the operation of the drop 290at-the atten ants position at the private branch exchange N. Theattendant answers the call by inserting the plug of a cord into the jackJ. This operation disconnects the drop 290 and closes a direct currentcircuit for the upper winding of ring cut-01f relay 41 2, causing thisrelay to operate and again lock to ring control conductor 407, and alsocausing t e extinguishment of lamp L. The attendant may now conversewith the toll operator,after which the two take the necessary steps toplace the distant calling subscriber and the called subscriber inconnection. a

At the termination of the conversation, the attendant removes the plugof her cord from the ack J, which causes the lighting of the lamp L asdescribed above, whereupon the toll o eratorremoves the plug P from thejack causing the release of the toll transmission selector TTS and thetoll second se lector TS in the manner reviously described. The removalof ground rom the release conductor 406 opens the circuit of relay 410,and the removal of ground from the ring control conductor 407 opens thecircuit of ring cutofl relay 412, whereupon these relays deenergize.Relay 410, in deenergizing, opens the circuit including the two windingsof relay 414 and relay 420, and by closing contacts 428 closes thecircuit of release magnet 422, Vertical oil-normal spring 473 havingbeen closed upon the first vertical step of the switch wipers. Releasemagnet 422 operates and restores the switch wipers to normal.

In order to describe the manner in which the toll rotary connector TRCselects the first locally busy trunk of a group, providing all thetrunks are either locally engaged or toll engaged, it will now beassumed that the toll operator has extended a toll connection via cordcircuit 0, the toll transmission selector TTS, the toll second selectorTS, to the toll rotarv connector TRC at a time when both the first andsecond trunks extending to the P. B. X. N are engaged in tollconnections and the trunk line comprising conductors 271 to 274 isengaged in a local connection, the local connection having been extendedto the P. B. X. N via local rotary connector LRC. (A detaileddescription of the operation of connector LRC is deemed unnecessarysince its vertical and rotary operation responsive to two di its dialledis similar to that of connector ll.) when used in a local connection,and its automatic trunk hunting operation is well-known, beingcontrolled by stepping relay 219 Which is operable in series withresistances such as R4 or R91, to be mentioned later.)

At this time, then, all three of the chain relays 494, 495, and 496 areoperated and the chain circuit connecting battery through resistance Rto test. contact 486 is closed. Also test contacts 486 and 487 are bothgrounded directly and test contacts 486 and 487' are grounded throughresistances, such as resistance R4, as shown at 6 and 6, Fig. 6. Theconditions on test contacts 489 and 489' are like that illustrated at 6,ground being connected to contact'489 by way of wiper 252 and sprin s250 of connector LRC.

Now, in this case, w en relay 415 falls back and closes contacts 451after the wipers of connector TRC have been rotated into engagement withthe 'set of contacts terminating the first trunk to P. B. X.. N,suflicient current will flow through the lower winding of test relay 418via resistance R96 to cause this relay to operate. In operating, relay418 closes a locking circuit for itself at contacts 463, connects wiper483 in the circuit of stepping relay 420 instead of wiper 482 byseparating contact 461 and closin tacts 462, and prepares the circuit orelay 414 at contacts 464.

An interval after relay 415 falls back, relay 416 falls back and startsthe rotary hunting operation. Switching relay 420 is operated fromground through resistances, such as resistance R4, connected to testcontact 486', and to test contact 487. Consequently, the switch wipersare rotated into engagement with the third set of bank contacts. Asassumed, the trunk terminating in the third busy set of bank contacts isbusy in a local connection, no ground connection appears on contacts489, but direct ground-is connected tobank contact 489. The value ofresistance R93 is high enough, however, to prevent sufficient currentflow through it and through the winding of stepping relay 420 to causerelay 420 to operate. Relay 420 therefore remains deenergized, and thewipers are arrested on this set of bank contacts. Busy relay 414 is alsoenergized over its lower wmdlng from ground on bank contact 489 viawiper 482 and contacts 464'and 459. In operating, relay 414 connectsground interrupter I to the upper talking conductor at contacts 444,opens a point in the circuit of switching relay 419 at contacts 445, andprepares a locking circuit to the ring control conductor 407 atcontacts447.

Upon the termination of the rotary operation, relay 417 falls back andopens a point of the circuit of switching relay 420 at contacts 457, andcloses the locking circuit for the lower winding of busy relay 414 tothe ring" control conductor 407 by permittin contacts 458 to close. Bythe separation 0? contacts operate to its second step and ing thedisconnection of line relay 411 from the trunkconductors; The tolloperator now receives the busy signal b the flashing of lamp L, thevinterrupter nected to the upper talking conductor, all as previouslydescribed.

The manner in which the toll operator as tabli shes a talking connectionto the engaged parties, and then forces a release of the localconnection in this type of connection is the same as when extending aconnectionto abusy individual subscribers line. The operator, bymomentarily'applying ringing current to the trunk conductors 3 and 4causes the deenergization of the differential busy relay 414. Relay 414deenergizes and closes the now being con-.

circuit of switching relay 419 which in oper- 3 and 4 causes groundpotential to be applied to the two talking conductors 8 and 6 whichunbalances the differential relay 218 in the ,local rotary connector LRGused in the local con-,-

connection. Relay 218 by closing contacts 223, closes a circuit forrelease magnet 242,

which in operating restores the wipers of connector LRC to normal. Thetoll operator is now connected to the private branch exchange over thethird trunk line, and the subscriber who was connected with the privatebranch exchange over this trunk line has been disconnected.

Should the toll operator wish to signal the attendant at the privatebranchexchange, she may do so in the regular way by applying ringingcurrent to the trunk conductors 3 and 4, which now causes the operationof relay 22 in the toll transmission selector TTS. Relay 22 by closingcontacts 77 and 74, applies ringing current to the trunk conductors tooperate the signal in the attendants cord circuit.

In the above case, it was assumed that the selected locallyengaged-trunk was busy in a connection extended to the P. B. X. N.'

Had this trunk been busy in a local connection initiated from the P. B.X. N, the first se- All nating the last trunk and into engagement withcontacts 491 492, 492, and 493, and will be arrested in this position,bank contact 492' being unequipped. Busy relay 414 is operated fromground connected to contact 492 through resistance R94, connectinginterrupter I to the upper talking conductor at contacts 444. Sincebattery potential through resistance R96 is connected to bank contact493 now engaged by switch wiper 484, the tone control relay in the tolltransmission selector also operates. Thus the operator not only receivesthe busy flash signal, but also receives a tone, indicating to her thatall the trunks to the private branch exchange are busy in tollconnections, whereupon she will release the connection and try again atsome later time. a

It is possible, after a toll rotary connector, such as connector THC, isrotated into engagement with the contacts terminating the first trunk ofthe group to a private branch exchange N, for example, and by itspreliminary tests has determined that there is an idle line in the group(indicated by the absence of battery connected through a resistance R95,on the test contact 486) that the only idle line existing at that timemay be seized by some other connector before the toll rotary connectorTRC can seize it. This last trunk will then also test busy, and the tollrotary connector TRC will continue to rotate over the other busy contactsets and into engagement with contacts 491, 492, 492' and 493. In such acase, of course, the busy relay 414 is not operated because relay 418has remained deenergized, and switching relay 419 will operateimmediately following the operas tion of relay 410. The toll operatornow receives the same, busy signals as when all the trunks are foundtoll engaged, since the interrupter I will now be connected to the uppertrunk conductor via bank contact 491 and wiper 481. The operator, asbefore, will again withdraw the plug of her cord to release the tollswitches operated, and redial the called number. In her second attempt,since now all the trunks are busy, she will obtain connection over thefirst locally busy trunk.

What is claimed is:

1. In a telephone system, a line which may be either idle or busy,switches including a selector and a connector for extending a connectionto said line, means for sending an impulse of ringing current to saidselector, and means in said selector responsive to an impulse of ringingcurrent, providing said line is busy in another connection, for causingthe release of said other connection.

2. In a telephone system, a line which may be idle or busy, switchesincluding a selector and a connector for extending a connection to saidline, means in said connector for signalling over said line, means forsending an impulse of ringing current to said selector,

means in said selector responsive to an impulse of ringing current forstarting the operation of said signalling means, providing the line isidle, and for causing the release of the connection in which said lineis engaged, providin said line is busy.

3. n a telephone system, a line which may be busy. or idle, switchesincluding a selector and a connector for extending a connection to saidline, means in saidconnector for signalling over said line, a switchingrelay in said connector for closing normally open contacts in thetalking circuit, means for sending impulses of ringing current to saidselector, means in said selector responsive to an impulse of ringingcurrent for starting the operation of said signalling means, providingthe line is idle when connection thereto is extended, and for causingthe operation of said switching relay, providing said line is busy whenconnection thereto is extended, and responsive to a second impulse ofringing current for causing the release of the connection in which saidline is engaged.

4. In a telephone system, a line which may be either idle or busy inanother connection, means including a selector, a trunk, and a connectorterminating the trunk for extending a connection to said line, means forsending ringing current to said selector, and means in said selectorresponsive to ringing current, providing said line is busy in anotherconnection when connection thereto is extended, for applying acharacteristic potential to the two talkin conductors of said trunk lineto cause the re ease of said other connection.

5. Ina telephone system, a line which may be either idle or busy inanother connection, means including a selector and a connector forextending a connection to said line, a relay in said connector operativewhen connection to the line is extended, providing said line is idle,for completing the talking connection from said selector to said line,means for sending impulses of ringing current to said selector, andmeans in said selector responsive to one impulse of ringing current forcausing the operation of said relay, providing said line is busy inanother connection when connection thereto is extended, and responsiveto another impulse of ringing current for causing therelease of saidother connection.

6. In a telephone system, a line which may be either idle or busy inanother connection, means including a selector, a trunk, and a connectorterminating said trunk line for extending a connection to said line, arelay in said connector for completing the talking connection to saidline automatically operative when connection to the line is completed,providing the line is idle, means in said selector for causing theoperation of said relay when said line is busy in another connection andfor causing the release of said other connection, the for mer operationbeing controlled over one conductor of said trunk line and the latterover another conductor of said trunk line.

7. In a telephone system, a line, means including a selector, a trunkline comprising two talking conductors and a non-talking conductor, anda connector terminating said trunk line for extending a connection tosaid line, a relay in said connector for completing the talkingconnection from said selector to said line, and means in said selectorfor controlling the operation of said relay over said non-talkingconductor, providing said line is busy in another connection whenconnection thereto is extended, and forcontrolling the release of saidother connection over a talking conductor of said trunk line.

8. In a telephone system, a line, means including a selector, a trunkcomprising two talking conductors and a non-talking conductor, and aconnector'for extending a connection to said line, a second connectorfor extending another connection to said line, a relay in said firstconnector operative to preventthe completion of the talking connectionwhen connection to said line is extended while the line is busy in saidother connection, and means in said selector for applying acharacteristic potential to said non-talking conductor to release saidrelay" to establish a talking connection to said line, even though theline is busy in said other connection, and for applying said potentialto one of said talking conductors, and means in said first connectorresponsive to the application of said potential to one of said talkingconductors for releasing said second connector.

9. In a telephone system, a line, a connector for extending a connectionto said line, a selector for extending a connection to said connector, aring control relay in said connector operated when a connection isextended to said connector, a busy relay in said connector forpreventing the'completion of the talking connection and for controllinga signal in case the line is busy when a connection thereto is extended,means for sending an impulse of ringing current to said selector, andmeans in said selector responsive to said impulse for causing therelease of said busy relay, providing it is operated, and for causingthe release of said ring control relay to signal over said line,providing the line is idle.

10. In a telephone system, a line, means including a selector, a trunk,and a connector terminating said trunk for extending a connection tosaid line, a first relay in said selector for disconnecting a normallyapplied potential from one conductor of said trunk, a second relay insaid selector for causing said normally applied potential to be appliedthrough a resistance, and means for making either relay efiectivedepending upon whether relay and a busy relay in said connector,

means in said selector for making either said first or said second relayefiective de ending on whether said line is busy or idle when connectionthereto is extended, means controlled by said first relay for controllinsaid ring control relay, and means controlled by; said second relay forcontrolling said busy re ay.

12. In a telephone system, a line, means including a selector, a trunk,and a connector terminating said trunk line for extending a connectionto said line, a ring control relay in said connector for controlling thesignalling of the subscriber on the line, a busy relay in said connectorfor controlling the operation of a busy signal, and means in saidselector for altering the character of the potential on one conductor ofsaid trunk line difi'erently depending on Whether the line is idle orbusy when connection thereto is extended to cause an operation of saidring control relay in one case and an operation of said busy relay inthe other case.

'13. In a telephone system, a line, means including a selector, a trunk,and a connector for extending a connection to said line, means in saidselector for altering the character of one conductor of said trunkdifferently depending on whether the line is idle or busy whenconnection thereto is extended, a ring control relay in said connectoreffected by one alteration, and a busy relay in said connector forcontrolling a busy signal effected by the other alteration.

14. In a telephone system, a line, means including a selector, a trunk,and a connector for extending a connection to said line, means forsending ringing current to said selector, means in said selectorresponsive to ringing current for altering the character of oneconductor of said trunk line difi'erently depending on whether the lineis busy or idle when connection thereto is extended, means in saidconnector responsive to one alteration for completing a talkingconnection providing the line is busy, and means in said connectorresponsive to the other alteration for signalling over said line,providing the line is idle.

15. In a telephone system, a line, a connector for extending aconnection to said line, a busy relay in'said connector having twowindings differentially wound, means for operating said relay over oneof its windings providing said line is busy when connection thereto isextended, and means for decreasing thecurrent in the one winding and forproducing a current flow in the other Winding to cause said bus relay todeenergize.

16. In a te ephone system, a line, an operators switchboard, a connectorfor extending a connection from said switchboard to said line, a busyrela in said connector having two windings difl rentially wound, meansfor operating said relay over one of its windings to prevent thecompletion of the talking connection providing said line is busy whenconnection thereto is extended, and operator controlled means forproducing equal values of current in the two windings of said relay tocause it to deenergize and complete the talking connection.

17. In a telephone system, a line, means including a selector and aconnector for ex tending a connection to said line, a busy relay in saidconnector having two windings differentially wound, means for operatingsaid relay over one of its windings to prevent the completion of thetalking connection providing said line is busy when connection theretois extended, and means in the selector for producing equal values ofcurrent in the two windings of said relay to cause it to deenergize andcomplete the talking connection.

18. In a telephone system, a line, a nonnumerical hunting switch, aplurality of numerical switches, means for successively operating saidswitches to extend a connection from said line, means for applying acharacteristic potential to a talking conductor of said line, and meansin the first numerical switch responsive to said application forreleasing said numerical switches while said hunting switch ismaintained operated.

19. In a telephone system, a line, a plurality of switches, means forsuccessively operating said switches to extend a connection from saidline, means for applying a characteristic potential to a talkingconductor of said line, means in one of said switches responsive to saidapplication for causing the release of a succeedin switch while apreceding switch is maintained operated.

20. In a telephone system, a line, a plurality of switches, means forsuccessively operating said switches to extend a connection from saidline, a differentially wound relay in one of the switches, means forapplying a characteristic potential to a talking conductor of said lineto operate said relay, and means controlled by said relay for causingthe release of a switch succeeding said one switch while a switchpreceding said one switch is maintained operated.

21. In a telephone system, a trunk comprising talking-conductors and arelease conductor, a connector having two directed movements forextending a call from said trunk, a relay in said connector operated atthe end of the first movement for conditioning said connector for itssecond movement,

a second relay in said connector operated when the call 1s answered, andmeans jointly controlled by said relays for momentarily applying acharacteristic potential to said release conductor.

22. In a telephone system, a trunk comprising talking conductors and arelease conductor, a connector having two directed movements forextending a call from said trunk, a relay in said connector operated atthe end of the first movement for conditionmg said connector for itssecond movement, and means controlled by said relay for applying acharacteristic potential to said reease conductor when the call isanswered.

23. In a telephone system, a toll trunk, a local trunk, a combinationtwo motion toll and local connector operable over either of said trunks,a relay in said connector operable at the completion of one motion tocondition said connector for its second motion, a two-step relay in saidconnector, means controlled by said first relay for operating saidtwo-step relay to its first step providing said connector is operatedover said toll trunk, and means operable at the completion of the secondmotion for operating said two-step relay to its second step, providingit has previously been operated to its first step, to condition saidconnector for toll operation.

24;. In a telephone system, a toll trunk, a local trunk, a combinationtwo motion toll and local connector operable over either of said trunks,a two-step relay in said connector, and means for operating said relayto its first step while the connector is executing its second motion andfor operating said relay to its second step at the completion of thesecond motion, providing the connector is operated over said toll trunk,to condition said connector for toll operation.

25. In a telephone system, a line which may be in either of threeconditions, a trunk, means including a connector for extending aconnection from said trunk to said line, means for distinctively markingone talking conductor of said trunk providing said line is in the firstor the second condition when connection thereto is extended, means fordistinctively marking the other talking conductor of said, trunkproviding said line is in the first condition when connection thereto isextended, and means operative in accordance with said markings forindicating the condition of said line.

26. In a telephone system, a line which may be idle, locally engaged ortoll engaged, means including a selector, a trunk, and a connectorterminating said trunk for extending a connection to said line, meansfor intermittently applying a characteristic potential to one talkingconductor of said trunk providing the line is toll or locally engaged,means for applying a characteristic potential to the other talkingconductor providing the 'line is toll engaged, and means in the selectorproviding said line is locally or toll engaged,-

means for distinctively marking another talking conductor of said trunkproviding said line is toll engaged, a signal at said switchboard, meansin said selector operative when one talking conductor is marked forcontrolling said signal, and means in said selector operative when theother talking con ductor is marked for giving the operator at saidswitchboard a distinctive tone.

28. In a telephone-system, a line, a contact for said line, means formarking said contact differently to indicate-the idle condition, thelocally busy condition,or the toll busy condition of said line, meansincluding a trunk for extending a connection to said line, a test relayoperative, providing said line is locally busy or toll busy whenconnection thereto is extended, to connect said contact to a conductorof said trunk, and means controlled over said conductor to' indicatewhether said line is locally busy or toll busy.

29. In a telephone system, a line, a test contact for said line, meansfor marking said contact differently to indicate the condition of saidline as to whether it is idle, locally busy or toll busy, meansincluding a trunk for extending a connection to said line, a test relayfor distinctively marking one conductor of said trunk and for connectingsaid contact to another conductor of said trunk providing said line islocally busy or toll busy when connection thereto is extended, and meanscontrolled over said two conductors for indicating the condition of saidline.

30. In a telephone system, a line, an operators switchboard, a testcontact for said line, means for marking said contact differently toindicate the idle condition, the locally busy condition, and the tollbusy condition of said line, means including a selector, a trunk, and

a connector for extending a connection from said switchboard to saidli'ne, an interrupter, a test relay in said connector for connectingsaid interrupter to one conductor of said trunk and for connecting saidcontact to another conductor of said trunk, a signal at saidswitchboard, means in said selector controlled over said one conductorfor operating said signal, and means in said selector controlled oversaid other conductor for giving the operator at said switchboard adistinctive tone providing said line is toll busy.

31. In a telephone system, a group of' lines,

any one or more of which may be idle, locally busy, or toll busy, arotary connector having two test wipers, and means including one of saidtest wipers for operating said connector to select an idle one of saidlines, providing one is idle, and including the other test wiper foroperating said connector to select a locally busy line providing all thelines are either locally busy or toll busy.

32. In a telephone system, a group of lines, any one or more ofwhich maybe idle, locally busy, or toll busy, a rotary connector having two testwipers, means controlled over either of said wipers for operating saidconnector, said means being effective to cause the connector to selectan idle line, providing one is idle, when controlled by one test wiperand effective to cause the connector to select a locally busy line,providing all the lines are either locally busy or toll busy, and meansoperative previous to the selecting operation, providing all the linesare either locally busy or toll busy, for determining which wiper is tocontrol the selecting operation.

33. In a telephone system, a group of lines, means for marking each ofsaid lines in accordance as to whether it is idle, locally busy, or tollbusy, means for further marking a certain one of said lines when all ofthe lines are either locally busy or toll busy, a rotary connectorhaving two test wipers, means controlled over either of said wipers foroperating said connector, said means being effective to cause theconnector to select an idle line, providing one is idle, when controlledby one test wiper and effective to cause the connector to select alocally busy line, providing .all the lines are either locally busy ortoll busy, and means operative in accordance with the marking on saidcertain one of said lines for determining which wiper is to control theselecting operation.

34. In a telephone system, a local rotary connector, a toll rotaryconnector, lines consecutively accessible to said connectors, two testcontacts for each line, means for distinctively marking the first testcontact of each line when the line is locally busy, and fordistinctively marking both test contacts of, each line when the line istoll busy, means in said local rotary connector controlled by themarkings on both test contacts of the lines preceding an idle line forcausing the local rotary connector to select the idle line, providingone is idle, and means in said toll rotary connector controlled by themarking on the first test contact of the lines preceding an idle linefor causing the toll rotary connector toselect the idle line, providingone is idle, and controlled by the marking on the second test contact ofthe lines preceding a locally busy line for causing the toll rotaryconnector to select the locally busy line, providing all the lines areeither toll busy or locally busy.

